1. Field of the Invention
This invention relates generally to electrical connectors for electronic devices. More particularly, the invention relates to electrical contacts for use in electrical connectors to prevent the generation of spurious signals upon mating of the connector.
2. Description of the Related Art
Electrical connectors for use with peripheral electronic devices are well known in the art. A recurrent problem with many prior art connectors is the generation of spurious signals upon mating of a peripheral electronic device to an electronic system which is already energized. The connector may induce a voltage pulse into the energized electronic system. The voltage pulse may travel through the electronic system, thereby introducing spurious errors into the system. This problem is known in the art as the "hot plug" problem.
This condition that causes errors in electronic systems results from the very high data rates and very low energy of the signals within the systems. The input capacitance of the connector, printed circuit board lines and device capacitance of the buffer integrated circuit devices are the basis of the problem. Energy must flow from the system bus to charge this input capacitance, (generally tens of picofarads). When energy is removed from the system bus, a voltage pulse to an adjacent device on the bus occurs, thereby creating errors in the system. The voltage pulse may be no greater than normal signals so no new radiated noise problem is introduced. However, it can cause data to be incorrectly transferred. Accordingly, the interconnections themselves are a large portion of the problem. This problem is universal since it affects both digital and analog electronic devices.
The prior art has generally addressed the "hot plug" problem by using logic and timing control circuitry, such as that which is disclosed in U.S. Pat. No. 4,245,270 to slowly ramp up the voltage within the connecting line. However, providing the additional circuitry is complex and expensive.
Many connecting schemes require certain portions of the connector to be mated prior to other portions, or in a particular sequence. For example, with respect to power applications, U.S. Pat. No. 4,079,440 discloses a circuit board having two connector plugs of differing lengths. The longer connector plug makes initial contact with a power line prior to the shorter plug, which reduces the onset of power surges. However, this scheme requires manual dexterity and specific insertion and removal timing for proper operation.
A connector assembly disclosed in U.S. Pat. No. 4,747,783 attempts to eliminate timing and control circuitry for power applications. This connector assembly uses a long pin in the "plug" to first make contact with its mating "socket" to gradually increase the voltage to the socket until the entire plug makes mating contact with the socket. The plug comprises a pin having a thin insulating material covering the surface and a thin low resistive material covering the insulating material. When the plug makes initial contact with the socket, the current must pass through the resistive portion of the plug. This permits the electronic components in the peripheral device to charge gradually and eliminates the current surges which may result.
This device is undesirable for several reasons. First, it requires the use of several contacts of differing lengths, thereby raising manual dexterity problems. Secondly, although the low resistance (i.e. 2-60 ohms) is sufficient to eliminate current surges in power transmissions, it is not sufficient to eliminate the voltage pulse from being introduced into the electronic system. In addition, the thin layer of low resistive material surrounding the thin layer of insulating material introduces an additional problem into the connection between the peripheral device and the electronic system; short capacitance. As explained previously, capacitance is undesirable in a connector.
It would be desirable to provide a signal connector assembly that would not introduce errors into an electronic system during a hot plug.